The present invention relates to a rectilinear motion apparatus for use in industrial robots or the like.
A conventional rectilinear moving apparatus will be described hereinbelow.
FIG. 11 indicates the basic structure of a conventional rectilinear moving apparatus disclosed in Japanese Laid-open Patent Publication No. 2-106283. In FIG. 11, a driving pulley 13 having the radius (r) is coupled to a driving motor 11 via a shaft 12a. A shaft 12b is set parallel to the shaft 12a and coupled with an idler pulley 14. An endless belt 15 connects the driving pulley 13 with the idler pulley 14. A slider 17 is arranged so as to be kept in contact with the endless belt 15 between the driving pulley 13 and the idler pulley 14.
The operation of the above-described conventional rectilinear moving apparatus will be explained now.
When the driving pulley 13 is rotated by an angle .theta. by the driving motor 11, the endless belt 15 is moved the distance r.theta., and the slider 17 alike is moved the same distance r.theta.. Therefore, the moving amount of the endless belt 15 by the rotation of the driving pulley 13 is equal to the moving amount of the slider 17 in the horizontal direction in the prior art arrangement.
If it is desired to decelerate the apparatus so as to augment the thrust and to improve the accuracy, conventionally, the apparatus disclosed in Japanese Laid-open Patent Publication No. 61-140665 is designed in such constitution as illustrated in FIG. 12. In FIG. 12, the shafts 12a, 12b are arranged parallel to each other, the former 12a coupling the driving motor 11 with the driving pulley 13, while the latter 12b is coupled to the idler pulley 14. The driving pulley 13 and the idler pulley 14 are connected with each other by the endless belt 15. There are provided two rotatable pulleys 20a, 20b and two pairs of guide rollers 18a, 18b and 18c, 18d in a slider 19 arranged between the pulleys 13 and 14. The lower run of the endless belt 15 is sent along the pulley 20a by the guide rollers 18a, 18b. On the other hand, the upper run of the endless belt 15 is retained by the guide rollers 18c, 18d to trace the pulley 20b. A pulley 21c is coupled with the pulley 20a by a shaft 22c, and is further coupled via an endless belt 23 with a pulley 21d connected with the pulley 20b by a shaft 22d. The pulley 21d has a smaller diameter than the pulley 21c.
The operation of the rectilinear moving apparatus of FIG. 12 will be described below.
When the driving motor 11 is driven, the driving pulley 13 is rotated, thereby rotating the idler pulley 14 and the pulleys 20a, 20b connected by the endless belt 15. Although the pulleys 21c, 21d coaxially provided with the pulleys 20a, 20b are rotated at this time, the pulley 20b coaxial with the pulley 21d assumes a larger rotating angle than the pulley 20a coaxial with the pulley 21c because the pulley 21d is smaller in diameter than the pulley 21c. Since the moving amount of the endless belt 15 is varied due to the difference of the rotating angles of the pulleys 20a, 20b, the slider 19 is moved half the difference of the moving amount. That is, the moving amount of the endless belt 15 subsequent to the rotation of the driving pulley 13 becomes half the difference of the diameter of the pulleys 21c and 21d.
Due to the number of pulleys present in the prior art as described above, the conventional apparatuses are disadvantageously complicated in structure and expensive, and the total loss of movement is large because of the backlash between each pulley and belt or the slack of the belts.